14,258 research outputs found
Encoding and Multiplexing of 2D Images with Orbital Angular Momentum Beams and the Use for Multiview Color Displays.
The orthogonal nature of different orbital angular momentum modes enables information transmission in optical communications with increased bandwidth through mode division multiplexing. So far the related works have been focused on using orbital angular momentum modes to encode/decode and multiplex point-based on-axis signals for maximum data channel numbers and capacity. Whether orbital angular momentum modes can be utilized to encode/decode off-axis signals for multiplexing in two-dimensional space is of significant importance both fundamentally and practically for its enormous potential in increasing the channel information capacity. In this work, a direct use of orbital angular momentum modes to encode/decode and multiplex two-dimensional images is realized in a scalable multiview display architecture, which can be utilized for viewing three-dimensional images from different angles. The effect of off-axis encoding/decoding and the resultant crosstalk between multiplexed different two-dimensional views are studied. Based on which, a color display of good image quality with four independent views is demonstrated. The resolution of the decoded images is analyzed and the limitation of this approach discussed. Moreover, a spatially multiplexed data communication scheme is also proposed with such a two-dimensional encoding/decoding approach to significantly enhance the data transmission capacity in free space for future data communication needs.UK Engineering and Physical Sciences Research Council (EPSRC) for the support through the Platform Grant for Liquid Crystal Photonics (EP/F00897X/1) and the EPSRC Centre for Innovative Manufacturing in Ultra Precision (EP/I033491/1
Detection of an X-ray Pulsar Wind Nebula and Tail in SNR N157B
We report Chandra X-ray observations of the supernova remnant N157B in the
Large Magellanic Cloud, which are presented together with an archival HST
optical image and a radio continuum map for comparison. This remnant contains
the recently discovered 16 ms X-ray pulsar PSR J0537-6910, the most rapidly
rotating young pulsar known.
Using phase-resolved Chandra imaging, we pinpoint the location of the pulsar
to within an uncertainty of less than 1 arcsec. PSR J0537-6910 is not detected
in any other wavelength band. The X-ray observations resolve three distinct
features: the pulsar itself, a surrounding compact wind nebula which is
strongly elongated and a feature of large-scale diffuse emission trailing from
the pulsar. This latter comet tail-shaped feature coexists with enhanced radio
emission and is oriented nearly perpendicular to the major axis of the pulsar
wind nebula. We propose the following scenario to explain these features. The
bright, compact nebula is likely powered by a toroidal pulsar wind of
relativistic particles which is partially confined by the ram-pressure from the
supersonic motion of the pulsar. The particles, after being forced out from the
compact nebula (the head of the ``comet''), are eventually dumped into a bubble
(the tail), which is primarily responsible for the extended diffuse X-ray and
radio emission. The ram-pressure confinement also allows a natural explanation
for the observed X-ray luminosity of the compact nebula and for the unusually
small X-ray to spin-down luminosity ratio, compared to similarly energetic
pulsars. We estimate the pulsar wind Lorentz factor of N157B as about 4 times
10^6 (with an uncertainty of a factor about 2, consistent with that inferred
from the modeling of the Crab Nebula.Comment: 15 pages plus 4 figures. The postscript file of the whole paper is
available at http://xray.astro.umass.edu/wqd/papers/n157b/n157b.ps. accepted
for publication in Ap
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Full bandwidth coarse integral holographic video displays with spatial tiling for scalability
Pressure dependence of the superconducting transition and electron correlations in Na_xCoO_2 \cdot 1.3H_2O
We report T_c and ^{59}Co nuclear quadrupole resonance (NQR) measurements on
the cobalt oxide superconductor Na_{x}CoO_{2}\cdot 1.3H_{2}O (T_c=4.8 K) under
hydrostatic pressure (P) up to 2.36 GPa. T_c decreases with increasing pressure
at an average rate of -0.49\pm0.09 K/GPa. At low pressures P\leq0.49 GPa, the
decrease of T_c is accompanied by a weakening of the spin correlations at a
finite wave vector and a reduction of the density of states (DOS) at the Fermi
level. At high pressures above 1.93 GPa, however, the decrease of T_c is mainly
due to a reduction of the DOS. These results indicate that the
electronic/magnetic state of Co is primarily responsible for the
superconductivity. The spin-lattice relaxation rate 1/T_1 at P=0.49 GPa shows a
T^3 variation below T_c down to T\sim 0.12T_c, which provides compelling
evidence for the presence of line nodes in the superconducting gap function.Comment: published on 19, Sept. 2007 on Phys. Rev.
Buy Now and Price Later: Supply Contracts with Time-Consistent Mean-Variance Financial Hedging
We consider a two-stage supply chain comprising one risk-neutral manufacturer (he) and one risk-averse retailer (she), where the manufacturer procures consumption commodities in spot market as major inputs for production and sells the final products to the retailer. The retailer then sells the final products to the market at a stochastic clearance price. We investigate a flexible price contract that allows the manufacturer to determine the product wholesale price, and the retailer to determine the order quantity, based on the future spot price of consumption commodities. Compared with the simple wholesale price contract, a win-win situation can be achieved under the flexible price contract when the manufacturer's postponed processing cost is lower than a threshold. However, under this flexible price contract the retailer may suffer from the commodity price volatility, even if she does not procure the commodities directly. We further investigate how the risk-averse retailer conducts mean-variance financial hedging by purchasing consumption commodity futures contracts. We formulate the problem using a dynamic programming model and derive a closed-form time-consistent financial hedging policy. Through numerical experiments, we show that the commodity price risk from the manufacturer to the retailer is effectively mitigated with the hedging, and the benefits of the flexible price contract are maintained
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